Basal Body Temperature Tracker

Basal Body Temperature (BBT) is the body’s resting temperature — measured first thing in the morning before getting out of bed, eating, or drinking. Tracking BBT daily is one of the most effective natural methods for identifying ovulation and the fertile window in a menstrual cycle.

How BBT Changes Through the Cycle

BBT typically follows a two-phase pattern:

• Pre-ovulation (Follicular Phase): Temperature is lower, typically 36.1°C – 36.4°C (97.0°F – 97.5°F)
• After Ovulation (Luteal Phase): Progesterone causes a temperature rise of about 0.2°C – 0.5°C (0.4°F – 0.9°F), remaining elevated for 10–16 days

Detecting Ovulation

Ovulation is confirmed when temperature rises at least 0.2°C (0.36°F) above the previous six days’ readings and stays elevated for three consecutive days. This is known as the “cover line” method.

Interpreting This Calculator

Enter your temperature for today along with your current cycle day. The calculator compares your reading to typical phase ranges and gives guidance on whether you are likely in the pre-ovulation or post-ovulation phase.

Practical Example (Celsius)

• Cycle days 1–14 (pre-ovulation): BBT around 36.2°C
• Cycle day 15: BBT rises to 36.6°C
• Cycle days 15–28: BBT stays above 36.5°C
• This sustained rise confirms ovulation occurred around day 14

Practical Example (Fahrenheit)

• Cycle days 1–14: BBT around 97.2°F
• After ovulation: BBT rises to and stays above 97.7°F

Tips for Accurate Readings

• Always measure at the same time each morning
• Use a dedicated BBT thermometer (reads to 0.01°)
• Avoid alcohol, illness, or poor sleep the night before — these raise BBT artificially
• Track for at least 2–3 cycles to see your personal pattern

BBT tracking works best when combined with cervical mucus observation for the most complete fertility awareness picture.